U.S. patent number 10,247,613 [Application Number 14/678,439] was granted by the patent office on 2019-04-02 for optical head tracking and object tracking without the use of fiducials.
This patent grant is currently assigned to ROCKWELL COLLINS, INC.. The grantee listed for this patent is David I. Han, Marvin R. Lovato, Daniel S. Wald, Brandon E. Wilson. Invention is credited to David I. Han, Marvin R. Lovato, Daniel S. Wald, Brandon E. Wilson.
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United States Patent |
10,247,613 |
Wald , et al. |
April 2, 2019 |
Optical head tracking and object tracking without the use of
fiducials
Abstract
A method of determining the angular orientation of headgear is
described. The headgear has tracking points being at least four
tracking points, the relative position of the tracking points is
calibrated and stored as relative position information, each of the
tracking points comprises an infra-red (IR) reflective point. Light
reflected from at least some of the tracking points of the headgear
is filtered to allow only light in an IR wavelength band to pass.
The filtered IR light is imaged to provide a detected image
including at least some of the tracking points. At least some of
the tracking points in the detected image are identified, and the
position of the identified tracking points in the detected image is
determined. The angular orientation of the headgear is determined
in multiple different angular directions based on the stored
relative position information and the position of the identified
tracking points.
Inventors: |
Wald; Daniel S. (Portland,
OR), Lovato; Marvin R. (West Linn, OR), Han; David I.
(Lake Oswego, OR), Wilson; Brandon E. (Portland, OR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wald; Daniel S.
Lovato; Marvin R.
Han; David I.
Wilson; Brandon E. |
Portland
West Linn
Lake Oswego
Portland |
OR
OR
OR
OR |
US
US
US
US |
|
|
Assignee: |
ROCKWELL COLLINS, INC. (Cedar
Rapids, IA)
|
Family
ID: |
65898600 |
Appl.
No.: |
14/678,439 |
Filed: |
April 3, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01B
11/26 (20130101) |
Current International
Class: |
G01J
5/10 (20060101); G01B 11/26 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Desta; Elias
Attorney, Agent or Firm: Suchy; Donna P. Barbieri; Daniel
M.
Claims
What is claimed is:
1. A method of determining the angular orientation of headgear, the
headgear having tracking points being at least four tracking
points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point, the
method comprising: filtering light reflected from at least some of
the at least four tracking points of the headgear to allow only
light in an IR wavelength band to pass; processing the filtered IR
light to provide a detected image including at least some of the at
least four tracking points; identifying at least some of the at
least four tracking points in the detected image, and determining
the position of the identified tracking points in the detected
image; and determining the angular orientation of the headgear in
multiple different angular directions based on the stored relative
position information and the position of the identified tracking
points.
2. The method of claim 1, wherein the determining the angular
orientation of the head gear comprises: determining a reference
plane corresponding to the identified tracking points based on the
stored relative position information and the position of the
identified tracking points.
3. The method of claim 1, wherein the determining the angular
orientation of the head gear comprises: determining the angular
orientation of the headgear in multiple different angular
directions based on the stored relative position information, the
position of the identified tracking points, and a calibrated
initial angular orientation of the head gear.
4. The method of claim 1, wherein each IR reflective point
comprises at least one of IR reflective tape or IR reflective
paint.
5. The method of claim 1, wherein the filtering light reflected
comprises filtering light reflected via an optical notch filter
passing light only in the IR wavelength band.
6. The method of claim 1, wherein the processing the filtered IR
light is performed via at least one of a camera or a focal plane
array.
7. The method of claim 1, wherein the headgear is at least one of
glasses, a head worn display, a helmet mounted display, or an
object requiring accurate three degrees of freedom or six degrees
of freedom in real time.
8. The method of claim 1, further comprising irradiating the
headgear with IR light.
9. The method of claim 1, wherein the multiple different angular
directions comprise yaw, pitch, and roll directions of the
headgear.
10. A method of calibrating an initial angular orientation of
headgear, the headgear having tracking points being at least four
tracking points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point, the
method comprising: aligning the headgear in a laboratory
environment; filtering light reflected from at least some of the at
least four tracking points of the headgear to allow only light in
an IR wavelength band to pass; imaging processing the filtered IR
light to provide a detected image including at least some of the at
least four tracking points; identifying at least some of the at
least four tracking points in the detected image, and determining
the position of the identified tracking points in the detected
image; determining the angular orientation of the headgear in
multiple different angular directions based on the stored relative
position information and the position of the identified tracking
points; and setting the determined angular orientation of the
headgear to be the initial angular orientation.
11. The method of claim 10, wherein the determining the angular
orientation of the head gear comprises: determining a reference
plane corresponding to the identified tracking points based on the
stored relative position information and the position of the
identified tracking points.
12. A device for determining the angular orientation of headgear,
the headgear having tracking points being at least four tracking
points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point, the
device comprising: a filter arranged to filter light reflected from
at least some of the at least four tracking points of the headgear
to allow only light in an IR wavelength band to pass; a detector
arranged to process the filtered IR light to provide a detected
image including at least some of the at least four tracking points;
and a processor configured to identify at least some of the at
least four tracking points in the detected image, to determine the
position of the identified tracking points in the detected image
and to determine the angular orientation of the headgear in
multiple different angular directions based on the stored relative
position information and the position of the identified tracking
points.
13. The device of claim 12, wherein the processor is configured to:
determine a reference plane corresponding to the identified
tracking points based on the stored relative position information
and the position of the identified tracking points.
14. The device of claim 12, wherein the processor is configured to:
determine the angular orientation of the headgear in multiple
different angular directions based on the stored relative position
information, the position of the identified tracking points, and a
calibrated initial angular orientation of the head gear.
15. The device of claim 12, wherein each IR reflective point
comprises at least one of IR reflective tape or IR reflective
paint.
16. The device of claim 12, wherein the filter comprises an optical
notch filter.
17. The device of claim 12, wherein the processing the filtered IR
light is performed via at least one of a camera or a focal plane
array.
18. The device of claim 12, wherein the headgear is at least one of
glasses, a head worn display, or a helmet mounted display, or an
object requiring accurate three degrees of freedom or six degrees
of freedom in real time.
19. The device of claim 12, further comprising an IR light source
configured to irradiate the headgear with IR light.
20. The device of claim 12, wherein the multiple different angular
directions comprise yaw, pitch, and roll directions of the
headgear.
Description
BACKGROUND
The present invention relates generally to the field of a method
and device for determining the angular orientation of headgear.
Tracking of the orientation of headgear, such as the headgear of an
aircraft pilot, is known. Head tracking can be achieved through
multiple means, most often in the form of magnetic tracking,
ultrasonic tracking, inertial tracking, optical tracking and hybrid
optical-inertial tracking.
Optical tracking can either be achieved through outside-in sensing
(where a system of cameras is mounted external to the object being
tracked with active/unique fiducials mounted on the object of
interest), or inside-out sensing (where a camera is mounted on the
object of interest and tracks active/unique fiducials of the
external scene).
SUMMARY OF THE INVENTION
According to one embodiment of the invention there is provided a
method of determining the angular orientation of headgear, the
headgear having tracking points being at least four tracking
points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point. The
method comprising: filtering light reflected from at least some of
the tracking points of the headgear to allow only light in an IR
wavelength band to pass; imaging the filtered IR light to provide a
detected image including at least some of the tracking points;
identifying at least some of the tracking points in the detected
image, and determining the position of the identified tracking
points in the detected image; and determining the angular
orientation of the headgear in multiple different angular
directions based on the stored relative position information and
the position of the identified tracking points.
According to one aspect of the embodiment, the determining the
angular orientation of the head gear comprises: determining a
reference plane corresponding to the tracking points based on the
stored relative position information and the position of the
identified tracking points.
According to another aspect of the embodiment, the determining the
angular orientation of the head gear comprises: determining the
angular orientation of the headgear in multiple different angular
directions based on the stored relative position information, the
position of the identified tracking points, and a calibrated
initial angular orientation of the head gear.
According to another aspect of the embodiment, each IR reflective
point comprises at least one of IR reflective tape or IR reflective
paint.
According to another aspect of the embodiment, the filtering light
reflected comprises filtering light reflected via an optical notch
filter passing light only in the IR wavelength band.
According to another aspect of the embodiment, the imaging the
filtered IR light is performed via at least one of a camera or a
focal plane array.
According to another aspect of the embodiment, the headgear is at
least one of glasses, a head worn display, a helmet mounted
display, or an object requiring accurate three degrees of freedom
or six degrees of freedom in real time.
According to another aspect of the embodiment, the method further
comprises irradiating the headgear with IR light.
According to another aspect of the embodiment, the multiple
different angular directions comprise yaw, pitch, and roll
directions of the headgear.
According to another embodiment of the invention there is provided
a method of calibrating an initial angular orientation of headgear,
the headgear having tracking points being at least four tracking
points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point. The
method comprising: aligning the headgear in a laboratory
environment; filtering light reflected from at least some of the
tracking points of the headgear to allow only light in an IR
wavelength band to pass; imaging the filtered IR light to provide a
detected image including at least some of the tracking points;
identifying at least some of the tracking points in the detected
image, and determining the position of the identified tracking
points in the detected image; determining the angular orientation
of the headgear in multiple different angular directions based on
the stored relative position information and the position of the
identified tracking points; and setting the determined angular
orientation of the headgear to be the initial angular
orientation.
According to one aspect of the embodiment, the determining the
angular orientation of the head gear comprises: determining a
reference plane corresponding to the tracking points based on the
stored relative position information and the position of the
identified tracking points.
According to another embodiment of the invention there is provided
a device for determining the angular orientation of headgear, the
headgear having tracking points being at least four tracking
points, the relative position of the tracking points being
calibrated and stored as relative position information, each of the
tracking points comprising an infra-red (IR) reflective point. The
device comprising: a filter arranged to filter light reflected from
at least some of the tracking points of the headgear to allow only
light in an IR wavelength band to pass; a detector arranged to
image the filtered IR light to provide a detected image including
at least some of the tracking points; and a processor configured to
identify at least some of the tracking points in the detected
image, to determine the position of the identified tracking points
in the detected image and to determine the angular orientation of
the headgear in multiple different angular directions based on the
stored relative position information and the position of the
identified tracking points.
According to one aspect of the embodiment, the processor is
configured to: determine a reference plane corresponding to the
tracking points based on the stored relative position information
and the position of the identified tracking points.
According to another aspect of the embodiment, the processor is
configured to: determine the angular orientation of the headgear in
multiple different angular directions based on the stored relative
position information, the position of the identified tracking
points, and a calibrated initial angular orientation of the head
gear.
According to another aspect of the embodiment, each IR reflective
point comprises at least one of IR reflective tape or IR reflective
paint.
According to another aspect of the embodiment, the filter comprises
an optical notch filter.
According to another aspect of the embodiment, the imaging the
filtered IR light is performed via at least one of a camera or a
focal plane array.
According to another aspect of the embodiment, the headgear is at
least one of glasses, a head worn display, a helmet mounted
display, or an object requiring accurate three degrees of freedom
or six degrees of freedom in real time.
According to another aspect of the embodiment, the device further
comprises an IR light source configured to irradiate the headgear
with IR light.
According to another aspect of the embodiment, the multiple
different angular directions comprise yaw, pitch, and roll
directions of the headgear.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a device for determining the angular
orientation of headgear, according to an embodiment of the
invention.
FIG. 2 illustrates tracking points, a reference plane, and normal
vector normal to the reference plane.
FIG. 3 illustrates the normal vector in xyz coordinate system also
showing yaw, pitch and roll angular rotations.
FIG. 4 is a schematic of an alignment device for calibrating the
headgear, according to an embodiment of the invention.
FIG. 5 is a flow chart illustrating a process of determining an
initial angular orientation of the headgear.
FIG. 6 is a flow chart illustrating a process of continuously
determining the angular orientation of the headgear in
operation.
FIG. 7 is a flow chart illustrating a process of determining the
angular orientation of the headgear of a step in the process of
FIG. 6.
DETAILED DESCRIPTION
According to certain described embodiments, the system includes an
optical filter which allows only light within an IR wavelength band
to pass to the detector, and the headgear has tracking points which
reflect light with an IR wavelength within the wavelength band.
The combination of tracking points with IR reflection points, and
allowing only IR light within a wavelength band to pass and be
detected, reduces the clutter of the scene in the vicinity of the
tracking points, particularly in the case where the clutter does
not reflect IR light within a wavelength band. The clutter is
reduced because only the IR reflecting tracking points are "seen"
by the detector and not the background clutter.
Tracking may be achieved using only a single detector, such as a
camera, and/or an FPA. Thus the complexity of the system may be
reduced.
Since the tracking is performed using tracking points which reflect
IR light, active fiducials or passive fiducials need not be used.
Fiducials, active or passive, are unique and identifiable, such as
bar codes. Foregoing fiducials reduces size, weight, power, and
cost associated with tracking systems which use active fiducials
mounted to track headgear. Since passive fiducials are not used,
the need to properly mount a large bar-code style passive fiducial
required for currently employed passive tracking algorithms is
eliminated. Further, since there is no need for unique fiducials, a
smaller form factor and easier sensor recognition can be
achieved.
Further, according to certain embodiments, the system is used with
stored relative position information (form factor), which provides
the relative position of the tracking points on the headgear. Thus,
the system is adaptable to any form factor attributed to a
particular headgear. This eliminates variability in the field and
simplifies user inputs. Moreover, placement of the IR reflecting
tracking points is not tightly constrained due to the use of
calibrated positional information, allowing for a more
manufacturable product than that using fixed fiducials typically
required for outside-in tracking systems.
FIG. 1 illustrates a device 100 for determining the angular
orientation of headgear 170. The device 100 includes an optical
filter 110, a detector 120, a processor 130, and optionally a light
source 140.
The device 100 determines the angular orientation of headgear 170
based on infra-red (IR) light reflected by tracking points 175 on
the head gear 170. FIG. 1 illustrates three tracking points 175 for
ease of illustration, but in general the number of tracking points
175 may be four or more. Each of tracking points 175 may comprise
an IR reflective point, which reflects IR light. The IR reflective
points may be, for example, IR reflective tape and/or IR reflective
paint. The relative position of the tracking points 175 is
calibrated, such in a laboratory environment, and is stored as
relative position information (form factor). The processor 130 has
access to the stored relative position information, such as via a
memory (not shown) internal or external to the processor 130.
The filter 110 is arranged to filter light reflected from at least
some of the tracking points 175 of the headgear to allow only light
in an IR wavelength band to pass. The filter 110 may be an optical
notch filter, for example. The combination of tracking points with
IR reflection points, and allowing only IR light in a wavelength
band to pass, reduces the clutter of the scene in the vicinity of
the tracking points, particularly in the case where the clutter
does not reflect IR light within a wavelength band. This concept is
similar to a "blue screen" where the blue is filtered out or not
detected, such that only a non-blue object in front of the blue
screen is imaged.
The detector 120 is arranged to image the filtered IR light 115 to
provide a detected image including at least some of the tracking
points 175. The detected image need not include all of the tracking
points 175, and will not in the case that the headgear 170 is
oriented that some of the tracking points are blocked from being
imaged due to the orientation of the headgear 170. That is, a
tracking point 175 will not be in the detected image in the case
that the detector 120 can not "see" that tracking point due to a
portion of the head gear 170, or some other object, blocking the
sight line from the tracking point to the detector 120.
While FIG. 1 illustrates the tracking points 175 only on a front of
the headgear 170, in general the tracking points 175 may be include
tracking points other than on the front, such as on the sides of
the headgear 170. This facilitates tracking in the case that the
headgear is rotated to the extent that a side of the headgear with
a tracking point becomes visible to the detector 120, and thus the
tracking point on the side may be tracked.
The detector 120 may be a camera and/or a focal plane array (FPA).
For example, the detector 120 may be a camera with an FPA, where
the FPA includes an array of pixels. The detector 120 may including
imaging optics, such as would be present with a camera.
The processor 130 may be configured to identify at least some of
the tracking points 175 in the detected image and determine the
position of identified tracking points 175 in the image. The
identification of tracking points 175 is aided because the
background clutter near the tracking points is reduced or
eliminated through the use filtering out the background clutter via
the filter 110, thus leaving only the tracking pints 175 in the
image.
The processor 130 may further be configured to determine the
angular orientation of the headgear 170 in multiple different
angular directions based on stored relative position information
and the position of the identified tracking points. The processor
130 may have a memory storing a program for determining angular
orientation, or include a circuit providing the structure to
determine the angular orientation.
The device 100 may optionally include a light source 140. A light
source 140 is not required since generally the ambient light
illuminating the head gear will be sufficient to reflect off of the
tracking points 175, and the reflection detected by the detector
120 to provide an image. The light source 140 may be a light
emitting diode (LED) or laser with a beam expander, for example,
emitting light within the wavelength pass band of the filter
110.
The processor 130 may be configured to determine a reference plane
corresponding to the tracking points 175 based on the stored
relative position information and the detected image, and to
calculate a normal vector normal to the reference plane.
The headgear 170 may be glasses, a head worn display (HWD), a
helmet mounted display (HMD), or an object requiring accurate three
degrees of freedom or six degrees of freedom in real time for
example. The headgear 170 may include an inertial motion unit (IMU)
which determines motion of the headgear 170.
FIG. 2 illustrates three tracking points 175 and a reference plane
200 corresponding to the tracking points 175. FIG. 2 illustrates
three tracking points 175 for ease of illustration, but in general
the number of tracking points 175 may be four or more. While the
reference plane 200 corresponds to the tracking points 175, one or
more of the tracking points 175 need not be in the reference plane
200. The relative position of the reference plane 200, however, is
fixed relative to the tracking points 175. Thus, when the tracking
points 175, which have a fixed position relative to each other,
rotate, the reference plane 200 may also rotate with the tracking
points 175 so as to maintain the fixed relationship with respect to
the tracking points 175.
FIG. 2 further illustrates a normal vector 210, which is normal
relative to the reference plane 200. Once the reference plane 200
is determined, its normal vector 210 may be readily determined. The
three dimensional rotation of the tracking points 175 may be
expressed in terms of the normal vector 210, which is perpendicular
to the reference plane 200, and the rotation of the tracking points
175 around an axis along the normal vector 210.
FIG. 3 illustrates the normal vector 210 in an (x,y,z,Y,P,R)
coordinate system. FIG. 3 discloses the three angular rotations of
yaw, pitch and roll (YPR), where yaw is the counterclockwise
rotation about the z axis, pitch is the counterclockwise rotation
about the y axis, and roll is the counterclockwise rotation about
the x axis. The three dimensional rotation of the tracking points
175 may be expressed in terms of YPR angular coordinates, for
example. Angular coordinate systems other than YPR angular
coordinates may also be used.
As mentioned above, the relative position of the tracking points
175 is calibrated and is stored as relative position information.
Thus a form factor (relative position information) for the tracking
points 175 is determined. Measuring the form factor may be
performed in a laboratory environment in an initial calibration.
The relative position information is stored, such as in a memory,
for later use in determining the relative angular orientation of
the headgear 170, based on tracking the tracking points 175.
Calibration may performed by knowing the true positions of the
tracking point 175 as measured in a calibrated laboratory
environment.
FIG. 4 illustrates an alignment device 300 for initially
calibrating the headgear 170 and determining the relative position
information, and for a process which includes physically aligning
the headgear 170. The device 300 of FIG. 4 is similar to the device
100 of FIG. 1, but further includes aligning equipment 410 upon
which the headgear 170 may be mounted where the aligning equipment
410 allows the headgear to be rotated to true positions. The
distance from the detector 120 to the aligning equipment 410 is
known in the calibrated setting.
The headgear 170 is angularly and possibly translationally moved to
bring the tracking points 175 into true positions. The angular
orientation of the headgear 170 when the tracking points 175 are in
true positions is considered to be an initial angular orientation.
The relative distances between the tracking points is determined
based on the known distances from the detector 120 to aligning
equipment 410, and based on the imaged tracking points 175.
Once the headgear 170 is physically oriented to the initial angular
orientation, operation of the device 100 is performed in a similar
fashion to that described with respect to FIG. 1. That is, light
from the tracking points 175 is filtered to allow only light in an
IR wavelength band to pass, the filtered IR light is imaged to
provide a detected image including at least some of the tracking
points 175, and at least some of the tracking points 175 in the
detected image are identified. The relative position information
(form factor) is determined based on the known distance from the
detector 120 to the aligning equipment 410, and the position of the
tracking points 175 on the detected image.
FIG. 5 is a flow chart illustrating steps in a process of
determining the initial angular orientation of the headgear 170
after the stored relative position information (form factor) of the
headgear has been determined. This process may be performed in a
headgear use environment, where a user has donned the headgear 170,
and where the detector 120 position has been calibrated. In step
S510, the reflected light from at least some of the tracking points
175 are filtered by the filter 110. In particular, light reflected
from at least some of the tracking points 175 is filtered to allow
only light in an IR wavelength band to pass.
In step S520, filtered IR light is imaged to provide a detected
image including at least some of the tracking points 175. The
imaging is performed using the detector 120.
In step S530, the tracking points 174 in the detected image are
identified.
In step S540, the position of the identified tracking points in the
detected image is determined.
In step S550, the processor 130 determines the angular orientation
of the headgear 170 in multiple different angular directions based
on the stored relative position information and the position of the
identified tracking points 175. The angular orientation may be
expressed in a YPR coordinate system, or any other appropriate
coordinate system. In particular, the reference plane corresponding
to the tracking points 175 may be determined based on the stored
relative position information and the position of the identified
tracking points 175. Once the reference plane is determined, a
normal vector normal to the reference plane may be readily
determined. Further the rotation of the tracking points 175 about
an axis along the normal vector may further be determined.
In step S560 the determined angular orientation of the headgear
170, as determined in step S550, is set to be the initial angular
orientation of the headgear 170.
FIG. 6 is a flow chart illustrating steps in a process of
continuously determining the angular orientation of the headgear
170 in operation. In step S610, the headgear 170 queries its
angular orientation to the device 100. In step S620, the angular
orientation of the headgear 170 is updated. If no angular
orientation of the headgear 170 is stored, the angular orientation
of the headgear 170 is set to the initial angular orientation of
the headgear 170.
In step S630, it is determined if the headgear 170 is in the field
of view (FOV) of the detector 120. In particular, if tracking
points 175 may be identified, then it is determined that the
headgear 170 is in the FOV. If the headgear 170 is determined to
not be in the FOV, the process returns to step S620. If the
headgear 170 is determined to be in the FOV, the process proceeds
to step S640 where the process of determining the angular
orientation of the headgear 170 is performed. Once the process of
determining the angular orientation of the headgear 170 is
performed in step S640, the process proceeds to step S620, where
the angular orientation of the headgear 170 is updated. The rate at
which the angular orientation of the headgear 170 is updated based
on the determining the angular orientation of the headgear 170 in
step S640, may be at about a 30 Hz rate, for example.
FIG. 7 is a flow chart illustrating steps in a process of
determining the angular orientation of the headgear 170 of step
S640 of FIG. 6. In step S710, the reflected light from at least
some of the tracking points 175 are filtered by the filter 110. In
particular, light reflected from at least some of the tracking
points 175 is filtered to allow only light in an IR wavelength band
to pass.
In step S720, filtered IR light is imaged to provide a detected
image including at least some of the tracking points 175. The
imaging is performed using the detector 120.
In step S730, the tracking points 175 in the detected image are
identified.
In step S740, the position of the identified tracking points in the
detected image is determined.
In step S750, the processor 130 determines the angular orientation
of the headgear 170 in multiple different angular directions based
on the stored relative position information and the position of the
identified tracking points 175. Further, the angular orientation of
the headgear 170 in multiple different angular directions may be
determined based on the initial angular orientation from step S560
of the process of FIG. 5, in addition to the stored relative
position information and the position of the identified tracking
points 175. In this case, in step S750, the angular orientation of
the headgear 170 may be determined relative to the initial angular
orientation.
The angular orientation may be expressed in a YPR coordinate
system, or any other appropriate coordinate system. In particular,
the reference plane corresponding to the tracking points 175 may be
determined based on the stored relative position information and
the position of the identified tracking points 175. Once the
reference plane is determined, a normal vector normal to the
reference plane may be readily determined. Further the rotation of
the tracking points 175 about an axis along the normal vector may
further be determined.
As mentioned above, according to certain described embodiments, the
system includes an optical filter which allows only light within an
IR wavelength band to pass to the detector, and the headgear has
tracking points which reflect light with an IR wavelength within
the wavelength band.
The combination of tracking points with IR reflection points, and
allowing only IR light within a wavelength band to pass and be
detected, reduces the clutter of the scene in the vicinity of the
tracking points, particularly in the case where the clutter does
not reflect IR light within a wavelength band. The clutter is
reduced because only the IR reflecting tracking points are "seen"
by the detector and not the background clutter.
Tracking may be achieved using only a single detector, such as a
camera, and/or an FPA. Thus the complexity of the system may be
reduced.
Since the tracking is performed using tracking points which reflect
IR light, active fiducials or passive fiducials need not be used.
Fiducials, active or passive, are unique and identifiable, such as
bar codes. Foregoing fiducials reduces size, weight, power, and
cost associated with tracking systems which use active fiducials
mounted to track headgear. Since passive fiducials are not used,
the need to properly mount a large bar-code style passive fiducial
required for currently employed passive tracking algorithms is
eliminated. Further, since there is no need for unique fiducials, a
smaller form factor and easier sensor recognition can be
achieved.
Further, according to certain embodiments, the system is used with
stored relative position information (form factor), which provides
the relative position of the tracking points on the headgear. Thus,
the system is adaptable to any form factor attributed to a
particular headgear. This eliminates variability in the field and
simplifies user inputs. Moreover, placement of the IR reflecting
tracking points is not tightly constrained due to the use of
calibrated positional information, allowing for a more
manufacturable product than that using fixed fiducials typically
required for outside-in tracking systems.
The embodiments of the invention have been described in detail with
particular reference to preferred embodiments thereof, but it will
be understood by those skilled in the art that variations and
modifications can be effected within the spirit and scope of the
invention.
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